Data from: Understanding the limits of binary diffusion for enhanced clay barrier design

Waste containment and isolation strategies often utilize bentonite as a
buffer material due to its swelling capacity, sealing efficiency, low
permeability and limited diffusive transport. However, previous
experimental studies of ionic diffusion through bentonite have shown
discrepancies with binary diffusion assumptions. Meticulous experiments
and complementary analyses reveal that the migration of preexisting ions
in the medium enables the differential flux of diffusing anions and
cations, while maintaining local electro-neutrality in all cases. The
separation between the cationic and anionic fronts is electrically tied to
the motion of the preexisting ions, and reflects the interplay between
valence, concentration, and self-diffusion coefficients of the ions
involved. Imposing binary diffusion conditions forces the faster anions to
diffuse at the same rate as cations. Therefore, effective barriers to
mitigate both cation and anion transport should have low surface charge
and low excess salts to minimize the preexisting ionic concentration.